Production of large diameter thin-walled tubing



April 1966 D. M. DOUTHETT ETAL 3,243,986

PRODUCTION OF LARGE DIAMETER THIN-WALLED TUBING Filed 001;. 1, 1963 DRAWBENCH PUSHBENCH Fi .2-E 2 o-o A u "4 ZO-l ho INVENTORS DELORMA M. DOUTHETT GEORGE MITCHELL BY their ATTORNEY United States Patent 3,243,986 PRODUCTION OF LARGE DIAMETER THIN-WALLED TUBING Delorma M. Douthett, Zelienople, Pa., and George A.

Mitchell, Youngstown, Ohio, assignors to Halstead Metal Products, Inc., Zelienople, Pa., a corporation of Pennsylvania Filed Oct. 1, 1963, Ser. N 312,987 9 Claims. (Cl. 72-283) This invention relates to a method and apparatus for producing tubing by cold-drawing techniques, and more particularly to the production of large diameter, thinwalled tubing from blooms of substantially the same diameter as they finished product but of increased wall thickness.

In the production of seamless metal tubing, a basic tubular shape or bloom of relatively short length and large wall thickness is initially produced by a hot extrusion or hot piercing operation. This bloom is then further worked by rolling, swaging or more commonly by cold drawing. Of course, a tubular shape of the desired inner and outer diameters can be produced directly by hot extrusion; however the resultin product is normally not of a quality that can be used in many applications because of non-concentricity, dimensional inaccuracies, rough surface finish, and softness.

All of the commonly used methods for working a thick-walled bloom to produce the finished product tend to decrease the outside diameter of the tube, making it smaller than the size of the original bloom. For example, in the case of cold-drawn tubing, the final outside diameter may be many times smaller than that of the original bloom; and as the shape is cold Worked and reduced in diameter during successive operations, successively smaller dies must be used each time the workpiece is drawn. Consequently, there is a direct relationship between the final outside diameter of the finished product and the size of the equipment needed to produce it, the larger the final desired outside diameter, the larger and more costly the equipment.

It is, of course, theoretically possible to produce a final product having an outer diameter in the range of about six inches if a bloom is originally employed having a starting diameter in the range of about one to two inches larger. This, however, requires extremely large and heavy equipment and also results in an excessive scrap loss.

In an effort to increase the capabilities of a particular cold-drawing installation to produce larger outside diameter tubing than can be manufactured by normal processes, arrangements have been devised for expanding the tube prior to cold working. The most conventional way to accomplish this is to force a plug or ball through the inside of the tube, thereby enlarging both the inside and outside diameters, slightly reducing the wall thickness, and shortening the tube. One end of the workpiece must then be pointed or swaged on a separate machine to provide a reduced diameter section which can be passed through the die of a drawbench and subsequently drawn through that die to reduce its outside diameter. This expansion and drawing procedure may be repeated several times to produce the desired finished tube outside diameter and wall thickness; however it requires three time-consuming and separate operations and also develops a relatively high percentage of scrap due to the length of the swaged end or point required on the large diameter tube prior to drawing.

As an overall object, the present invention seeks to provide a new and improved method for producing large diameter thin-walled tubing from blooms having an outer diameter substantially equal to, or even less than, that of the finished product.

More specifically, an object of the invention is to provide a method for producing cold-drawn, large diameter and thin-walled tubing from blooms of substantially the same diameter but increased wall thickness, which method overcomes the aforementioned and other disadvantages of prior art methods.

A further object of the invention is to provide a method for producing large diameter thin-walled tubing wherein no pointing or swaging of tube ends is required prior to drawing. This not only completely eliminates the swaging operation but also reduces the length of the scrap end of the tube gripped by the draw carriage during the drawing operation.

Still another object of the invention is to provide a method for producing large diameter thin-walled tubing by cold-drawing techniques wherein only a single die of fixed diameter is required for all drawing operations.

In accordance with the invention, a plug is initially forced into one end of a bloom and axially along the inner periphery of the bloom to the other end of the bloom, but not entirely therethrough, to thereby expand the bloom and increase its inner and outer diameters except at said other end to provide a non-expanded portion which can be passed through a drawbench drawing die. After the expansion operation, and with the tapered plug remaining in the bloom, the non-expanded diameter forward end of the bloom is gripped by a draw carriage and the workpiece drawn through the die which has a diameter substantially equal to or larger than the original diameter of the bloom prior to expansion. This produces a product having an outer diameter at least equal to the original diameter of the bloom, an inner diameter and length greater than that of the original bloom, and a wall thickness less than that of the original bloom. By repeating the foregoing process with plugs of successively larger diameters, the inner diameter of the workpiece will be gradually enlarged; however the outer diameter will remain constant for the reason that it is always drawn through a die of the same diameter after each expanding operation. The invention, however, is not limited to the use of a single die for all drawing operations since it may be desirable to employ dies of different diameters to increase the range of final sizes which can be produced on a single piece of equipment.

Further, in accordance with one embodiment of the invention, the apparatus for carrying forth the foregoing method comprises a pushbench and a drawbench arranged in end-to-end relationship with an intermediate die stand and common power supply. The extruded or pierced bloom is dropped into position on the pushbench bed, and its leading end moved against a stop plate mounted in position in front of the die of the aligned drawbench. Hold-down clamps are brought to bear on top of the tube and a floating-type draw plug is placed in alignment with the trailing end of the tube. Thereafter, a long cylindrical push rod attached to a push carriage forces the plug through the inside of the tube to enlarge its inside diameter to correspond with the maximum diameter of the tapered draw plug. The outside diameter of the tube also grows almost in the same proportion as the enlargement of the inside diameter; while the wall thickness and length decrease. As a specific example, the plug may be pushed within four or five inches of the leading end of the tube; and at this point the stop plate is moved from in front of the die and the remaining stroke of the push carriage moves the forward end of the bloom, which has not been expanded, through the drawing die where it is gripped by gripper jaws on a drawbench draw carriage which moves away from the die to thereby pull the tube through 3 the die while reducing its outside diameter and increasing its length.

The combination pushbench-drawbench of the invention is such that while the push carriage is engaged in a power stroke traveling toward the die plate,.the draw carriage is also returned toward the die plate. Thereafter, at the completion of the push stroke, the leading end of the tube is gripped by the draw carriage, which is then positioned in front of the die plate, and the power unit is reversed. The draw carriage-then pulls the tube through the die and the push carriage is returned to its retracted position preparatory to the next expanding operation. Thus, the time required to prepare the equipment for a subsequent expanding and drawing operation is minimized, and the equipment is simplified by virtue of the fact that only a single prime mover is required.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the .accompanying drawings which form a part ofthis specification, and in which:

FIGURE 1 is a schematic illustration of one embodiment of the invention; and

FIGS. 2A-2F are diagrams showing the successive steps of operation ofthe invention.

Referring now to the drawings, and particularly to FIG. 1, the combination pushbench-drawbench of the invention is shown and includes a die stand which carries a die 12 through which workpieces are drawn. The workpiece 14 comprises an extruded or pieroed'bloom which is clamped in position by means of a series of holddown clamps 16 spaced along the axis of the bloom 14. The clamps 16 will permit expansion of the bloom during the push stroke and serve, more or less, only to reduce thelength-over-radius ratio, and prevent buckling of the bloom during the push stroke. In order to prevent axial movement of the bloom during an expanding operation, a stop plate 18 is inserted between the leading end of the bloom 14 and. the die 12.

In order to expand the-bloom 14, a combination drawing. and expanding plug 20 is forced into its right or trailing end by means of a push rod .22 attached to a push carriage 24 which travels on a trackway 26. The-plug 20 is tapered, its minimum diameter end being initially inserted into the end of the bloom 14 followed by its maximum diameter end.

On the side of the die. 12.-opposite the push carriage 24 is adraw carriage 28 which travels along a guideway or track 30. As is well known to those skilled in the art, a draw carriage comprises a dolly or buggy which is V 7 provided with gripping jaws adapted to engage the nonexpanded diameter. end of a workpiece, such as bloom 14, which is inserted through the die 12.v One specific exampleof such grippingjaws, not shown herein, may be had by reference to US. Patent No. 2,861,679 issued to G. A. Mitchell on November 25, 1958. After the gripping jaws on the draw carriage 2S engage the forward end of the. workpiece, the draw carriage is moved awayfrom thedie, thereby pulling the workpiece through the die while reducing its outer diameter and increasing its length. The inner diameter of the workpiece is determined during the drawing operation by a floating element which, in the present case, comprises the combination drawing and expanding plug 20 as will hereinafter be explained.

The push carriage 24-and the draw carriage 28 are actuated by means ofa double-acting, double rod hydraulic cylinder 32. The cylinder includes a piston 34 disposed between two variable volume chambers 36 and 38. Means, not shown, are provided for forcing fluid under pressure into one of the variable volume chambers 36 or 38 while exhausting fluid from the other chamber whereby the piston 34 may be forced to the right or left, as the case may be.

The piston 34 is connected to two piston rods 40 and Cir 42, the piston rod 40 being connected through a clevis to a pulley or sheave 44, thepiston rod 42. being.con-. nected through a similar clevis to a pulley or sheave 46. The sheaves 44 and 46 are utilized in combination with a distance-multiplying cable arrangement for the purpose of moving both the push carriage 24 and draw carriage 28 toward or away from the die 12simultaneously, The cable arrangement includes a first cable 48 which is secured at 50 to the die stand 10. This cable passes around the sheave 44- and thence around a second sheave 54 supported on the die stand 16 'with the other endofthe cable 48 beingconnectedto the push carriage 24 as at 56. cylinder 32 is pressurized, the piston 34 will move to the right as viewed in FIG. 1, thereby forcing the push carriage 24 to the left. In this process, the push'rod 22 engages the plug 20-which, in turn, is-forced-in'toi the interior of the bloom 14 to expand it while increasing both its inner and outer diameters.

The push carriage 24-has connected theretoa cable'58 which passes around a sheave 60 supported on a mem-" ber 62 at the right end'of the apparatus. The cable 58 is connected to the draw carriage 28 as at 64, the'arrangement being such that as the push carriage 24is moved toward the die 12 during its power stroke whenthe plug 20-is forced into the bloom 14, the draw carriage 28twill also be moved along track 30 towardthe die 12'preparatory to a succeeding drawing operation. During this time, however, the only force needed to return the draw carriage 28 to the die is that necessary to overcome the inherent weight and frictional resistance of the draw carriage 28':

The draw carriage 23is also connected'toa cable: 66 which passes around sheave 68 at the left end of the apparatus and thence around sheave 70'on' member 62iand sheave 46 to point 71 where it is anchored on the member 62. As the draw carriage 28 is moved'to the right during the power stroke of the push carriage 24, the piston 34 of cylinder 32 will move to the right, thereby also moving sheave 46 to the right to permit the cable 661to' follow the draw carriage 28.

During the expanding operation, the plug 20' is forced axiallyv along the interior of the bloom '14 to apointwh'ere it is at the left end of the bloom. In this process,.the entire length of the bloom will be expanded except at its left end where it is not expanded due to. the fact that the plug 20 has not passed through the left end'of the bloom 14. At this point, the stop plate 18 isiremoved the clamps 16 released, and the. cylinder 32 actuated to move carriage 24, bloom 14 and the plug 20 carried-thereby to the left whereby the end of the bloom .which has not been expanded will extend through the die 12. Thereafter, the gripper jaws on draw carriage 28 are actuated to engage the non-expanded end of the bloom 14; and the variable volume chamber 36 of the cylinder 32 is pressurized to thereby move both the draw carriage 28 and the push carriage 24 away from the die 12 in opposite directions. During this time, the major portion of the power, supplied by cylinder 32 is applied to the draw carriage 28 which draws the bloom'14 through the die 12 while reducing its outer diameter and increasingits length.v The inner diameter of thebloom 14, however, is not materially reduced due to the fact that it is oontrolledby the plug 2% which remains within the workpiece as a floating draw: ing plug element.

If necessary to prevent collapse of the forward end of the tube when gripped by the gripper jaws of the draw carriage, an air cylinder-operated mandrel may be provided on the draw carriage which is inserted into, and supports, the forward end of the tube just prior .to the time that the gripper jaws engage the tube.

During the drawing operation, the plug 20- floats within the die opening rather than being sucked therethrough due to the relationship betweenthe lead-in angle of the die opening and the angle of the tapered surface of the plug with its axis. As is well known to those skilled in Thus, when the variable volume. chamber 38 of I 5 the art, this relationship may best be determined empirically from experimental data obtained by testing plugs of various taper angles for a particular die configuration.

At the completion of the drawing operation, the workpiece 14 will jump forwardiy and be automatically released by the gripper jaws of the draw carriage 28 while the plug 20 will fall out of the trailing end of the workpiece and may be used again. At the same time, the mandrel on the draw carriage, if employed, will be retracted from the non-expanded end of the bloom to permit it to fall into a receiving trough in accordance with usual drawbench practice. Following the drawing operation, the workpiece 14 is returned to the clamps 16, and a plug of larger maximum diameter is forced into the workpiece 14 to repeat the foregoing process. That is, the inner and outer diameters of the workpiece 14 are again expanded, but during the succeeding drawing operation the outer diameter of the workpiece is reduced to its original value, assuming the samesized die is used. By utlizing successive floating plugs 20 of progressively larger maximum diameters, it will be appreciated that the end result is a tube having an inner diameter much larger than that of the original bloom 14, but an outer diameter slig tly larger than that of the bloom 14, with the overall length of the workpiece being increased.

Operation of the apparatus shown in FIG. 1 may best be understood by reference to FlGS. ZA-ZF. Thus, the starting positions of the various elements are shown in FIG. 2A with the draw carriage 28 and push carriage 24 being at their positions furthest removed from the die 12. The bloom 14 is positioned between the end of push rod 22 and the die 12; the plug 20 inserted into the right end of the bloom 14; and the stop plate 18 inserted between the die 12 and the left end of bloom 14. At this time the bloom 14 has an outside diameter OD1, and a relatively small inside diameter ID-l. Plug 26 has a minimum diameter portion 21 which is initially inserted into the bloom 14, a tapered portion 23 and a maximum diameter portion 25 of diameter larger than the inner diameter ID-l of the bloom.

As the push carriage 24 is forced toward the die 12, it will also force the plug 2% into the interior of the bloom 14 as shown in FIG. 28, with the draw carriage 28 being moved toward the die 12 at the same time. In this process, both the inner and outer diameters of the bloom 14 are increased. Thus, the outside diameter of the bloom is now OD-2 and the inside diameter is ID-Z, which is substantially of the same diameter as portion 25 of plug 2G. The plug 26, however, is not forced through the entire length of the bloom 14 but stops in the position shown in FIG. 2B to provide a section 72 at its left end which is not expanded and has an outer diameter equal to O-D-1. Following this step, the stop plate 18 is removed and the push carriage 24 and draw carriage 28 moved further toward the die 12, thereby forcing the non-expanded end 72 of the bloom 14 through the die where it is gripped by gripper jaws on the draw carriage 28. The cylinder 32 is now reversed and the draw carriage 28 moves away from the die, thereby pulling the workpiece or bloom 14 through the die while decreasing its outer diameter and increasing its length as shown in FIGS. 2C and 2D. The inside diameter of the expanded bloom 14, however, is not materially decreased due to the fact that the plug 20 remains in the bloom during the drawing operation and controls the inner diameter. This operation continues until a point is reached as shown in FiG. 2E where the plug 20 drops out of the end of the drawn bloom 14, and the bloom is released by the gripper jaws of the draw carriage 2 8. The product now has an outside diameter slightly larger than the original outside diameter OD-i but an inside diameter lD-3 which is some-what less than the diameter ID-2 but larger than the original inside diameter ID- 1. The overall effect, therefore, has been to materially increase the inner diameter and length of the workpiece while only slightly increasing its outside diameter.

In FIG. QLF, the reltaionship of the parts are the same as those shown in FIG. 2A; however in this case a plug 29 1 of larger maximum diameter is forced into the right end of the bloom 14. This, of course, will create an inside diameter larger than ID-3 and also an increased outer diameter. in the subsequent drawing operation, however, the outside diameter is again reduced to slightly large than (FDA, but the inside diameter remains larger than 133-3. This process is repeated as many times as necessary in order to produce the required inside diameter and wall thickness.

Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention. In this respect, it will 'be apparent that by providing a die having a diameter materially larger than that of the original bloom, a final product can be produced which will also have a larger outside diameter for the reason that the bloom is always expanded during the push stroke. Furthermore, it will be appreciated that in an actual production operation, a plurality of blooms will be processed with the same sized plug followed by processing of all blooms by the next-larger plug rather than completing all expanding and drawing operations on a single workpiece before proceeding with the next.

We claim as our invention:

1. 1n the method for producing tubular shapes of predetermined inner and outer dimensions from thick-walled tubular blooms, the steps of first expanding both the inner and outer dimensions of said :bloom along its entire axial length except at one end thereof whereby the expanded outer dimensions will be at least slightly larger than said predetermined outer dimensions, thereafter passing said one end of the bloom which has not been expanded through a drawing die having a perimeter of dimensions substantially equal to said predetermined outer dimensions, and finally drawing the 'bloom through the die to thereby produce a product having outer dimensions substantially equal to said predetermined outer dimensions but a length greater than that of the original bloom.

2. In the method for producing thin-walled tubular shapes of predetermined inner and outer diameters from thick-walled tubular blooms, the steps of forcing a tapered plug into one end of the bloom and axially along the inner periphery of the bloom to the other end of the 'bloom but not entirely through the bloom to thereby initially expand the bloom and increase its inner and outer diameters along its entire axial length except at said other end of the bloom, the expanded outer diameter being at least slightly larger than said predetermined outer diameter, and thereafter drawing the bloom through a drawing die having a diameter substantially equal to said predetermined diameter with the tapered plug acting as a floating drawing element to thereby produce a product having an outer diameter substantially equal to said predetermined diameter, an inner diameter and length greater than that of the original bloom, and a wall thickness less than that of the original bloom.

3. The method of claim 2 wherein the tapered plug has a minimum diameter less than the inner diameter o f the original bloom and a maximum diameter greater than the inner diameter of the original bloom, and wherein the tapered plug is forced into said one end of the bloom with its maximum diameter portion trailing its minimum diameter portion.

4. In the method for producing thin-walled tu'bular shapes of predetermined inner and outer diameters from thick-walled tubular blooms, the steps of forcing a tapered plug into one end of the bloom and axially along the inner periphery of the bloom to the other end of the i bloom but not entirely through the. bloom to thereby expand the bloom and increase its inner and outer diameters except at said other end ofv the bloom, the expanded outer diameter'bein-g at least slightly larger than said predetermined outer diameter, drawing the bloom through a die having a diameter substantially equal to said predetermined diameter with the first tapered plug acting as a heating drawing element to thereby produce a product having an outer diameter substantially equal to said predetermined diameter but an inner diameter greater than that of the original bloom, forcing a second tapered plug having a maximum diameter greater than said first tapered plug into one end of the bloom and axially along the inner periphery of the bloom to the other end of the bloom but not entirely through the bloom to thereby expand the "bloom and increase its inner and outer diameters except at the other end of the bloom, and finally drawing the bloom through a die also having a diameter equal to said predetermined diameter with the second tapered plug acting as a floating drawing element to thereby produce a product having an outer diameter again substantially equal to said predetermined diameter, an inner diameter and length greater-than that of the product produced by the first drawing operation, and a wall thickness less than that of the product produced by the first-mentioned drawing operation.

5. The method of claim 4 wherein the same die is used during the first and second drawing operations.

6. In the method for producing thin-walled tubular shapes of predetermined inner and outer diameters from thick-walled tubular blooms, the steps of clamping the bloom such that it can expand radially but cannot move axially, forcing a tapered plug into one end of the clamped bloom and axially along the inner periphery of the bloom to the other end of the bloom but not entirely through the bloom to thereby expand the bloom radially and increase its inner and outer diameters except at said other end of the bloom, the expanded outer diameter being at least lightly larger than said predetermined outer diameter, releasing said bloom and passingsaid other end of the bloom which has not been expanded through a drawing die having a diameter substantially equal to said predetermined diameter, and finally drawing the bloom through the die with the tapered plug acting as a floating drawing element to thereby produce a product having an outer diameter substantially equal to said predetermined diameter, an inner diameter and length greater than that of the original bloom, and a wall thickness less than that of the original bloom.

7. A method for producing tubular products on apparatus including a drawing die, a draw carriage movable toward and away from the die on one side thereof, and a pus-h carriage movable toward and away from the die on the other side thereof: which comprises simultaneously moving the draw carriage and push carriage away from the die in opposite directions, positioning a tubular bloom in axial alignment with the die at the other side thereof and clamping the bloom to prevent its movement toward the die, inserting the reduced diameter end of a tapered plug into the end of the bloom opposite the die, causing said push carriage and draw carriage to simultaneously move toward the die with the push carriage engaging and forcing said tapered plug into the bloom to expand its inner and outer diameters, stopping movement of the draw carriage and ush carriage at a point where the plug has expanded all but the leading end portion of the bloom, releasing said bloom and again simultaneously moving the draw carriage and push carriage toward the die to cause the leading end portion of the bloom to pass through the die, gripping said leading endrportion of the bloom wtih the draw carriage, and simultaneously moving the draw carriage and the push carriage away from the die in opposite directions whereby the draw carriage will draw the bloom through said die with the tapered plug acting as a floating drawing element.

8. A method for producing tu bular products on apparatus including a drawing die, a draw carriage movable toward and away from the die on one side thereof, and a push carriage movable toward and away from the die on the other side thereof: which comprises simultaneously moving the draw carriage and push carriage away from the die in opposite directions, positioning a tubular bloom in axial alignment with the die at the other side thereof, placing a stop plate between the die and the end of the bloom adjacent the die whereby the stop plate will limit axial movement of the bloom toward the die, inserting the reduced diameter end of a tapered plug into the end of the bloom opposite the die, causing said push carriage and draw carriage to simultaneously move toward the die with the push carriage engaging and forcing said tapered pluginto the bloom to expand its inner and outer diameters, stopping movement of the drawcarriage and push carriage at a point where the plug has expanded'all 'but the leading end portion of the bloom, removingsaid stop plate from between the die and the forwardend of the bloom and again simultaneously moving the draw carriage and push carriage toward the die, to advance ,said leading end portion of the bloom through the die, causing the draw carriage to grip the leadingend portion ofthe bloom projecting through the die, and simultaneously movingthe draw carriage and push carriage away from the die to cause the drawcarriage to pull the bloom through the die. a

9. A method for producing tubular products on apparatus including a drawing die, a draw carriage movable toward and away from the die on one side thereof, and .a push carriage movable toward and away from the die on the other side thereof: which comprises movingthe push carriage away from the die, positioning a tuibularbloom in axial alignment with the die at the other side thereof and clamping the bloom to prevent its'movement. toward the die, inserting the reduced diameter end of a tapered plug into the end of the bloom opposite the die, causing said push carriage to move toward the die with the push carriage engaging and forcing said tapered plug into the bloom to expand its inner and outer diameters, stopping movement of the push carriage at a point where the plug has expanded all but the leading end portion of the bloom, releasing said bloom and again moving the push carraige toward the die to thereby forward said leading end portion through the die, causing said drawcarriage to grip said leading end portion of the bloom which projects through the die, and causing said draw carriage tomove away from the die to thereby pull the bloom through the die.

References Cited by the Examiner UNITED STATES PATENTS 7 307,993 11/1884 Sharp 72283 1,124,757 1/1915 Lloyd 722.78 1,973,031 9/1934 Wrage 72,27-8 2,234,863 3/1941 Heetkamp 7237.0 2,965,965 12/1960 Allan 72367 3,173,195 3/1965 Grimm 72367 CHARLES W. LANHAM, Primary Examiner.

H. D. HDINKES, Examiner. 

1. IN THE METHOD FOR PRODUCING TUBULAR SHAPES OF PREDETERMINED INNER AND OUTER DIMENSIONS FROM THICK-WALLED TUBULAR BLOOMS, THE STEPS OF FIRST EXPANDING BOTH THE INNER AND OUTER DIMENSIONS OF SAID BLOOM ALONG ITS ENTIRE AXIAL LENGTH EXCEPT AT ONE END THEREOF WHEREBY THE EXPANDED OUTER DIMENSIONS WILL BE AT LEAST SLIGHTLY LARGER THAN SAID PREDETERMINED OUTER DIMENSIONS, THEREAFTER PASSING SAID ONE END OF THE BLOOM WHICH HAD NOT BEEN EXPANDED THROUGH A DRAWING DIE HAVING A PERIMETER OF DI- 